Systematics, phylogeny and palaeobiogeography of the ankylosaurid dinosaurs

The Ankylosauria is a group of herbivorous, quadrupedal, armoured dinosaurs subdivided into at least two major clades, the Ankylosauridae and the Nodosauridae. The most derived members of Ankylosauridae had a unique tail club formed from modified, tightly interlocking distal caudal vertebrae and enlarged osteoderms that envelop the terminus of the tail. We review all known ankylosaurid species, as well as ankylosaurs of uncertain affinities, in order to conduct a revised phylogenetic analysis of the clade. The revised phylogenetic analysis resulted in a monophyletic Ankylosauridae consisting of Ahshislepelta, Aletopelta, Gastonia, Gobisaurus, Liaoningosaurus, Shamosaurus and a suite of derived ankylosaurids (Ankylosaurinae). There is convincing evidence for the presence of nodosaurids in Asia during the Early Cretaceous. In the mid Cretaceous, Asian nodosaurids were replaced by ankylosaurine ankylosaurids. Ankylosaurines migrated into North America from Asia between the Albian and Campanian, where they diversified into a clade of ankylosaurines, here named Ankylosaurini, characterized by arched snouts and numerous flat cranial caputegulae. There is no evidence for any ankylosaurids in Gondwana; Ankylosauridae appears to be completely restricted to Asia and North America. The genus Crichtonpelta gen. nov. is created, type species Crichtonsaurus benxiensis Lu et al. [GRAPHICS]